JP6164428B2 - Slip rate control device for four-wheel drive vehicles - Google Patents

Description

  The present invention relates to a slip ratio control device for a four-wheel drive vehicle that transmits a prime mover output torque output from a prime mover as a vehicle drive source to front wheels and rear wheels, and in particular, a part of the prime mover output torque is coupled via a coupling. The present invention relates to a slip ratio control device for a four-wheel drive vehicle that can change the torque transmitted to the rear wheels out of the motor output torque by transmitting the torque to the rear wheels and changing the coupling torque of the coupling.

  Conventionally, there has been proposed control for distributing the driving torque from the prime mover to the front wheels and the rear wheels in consideration of the slip ratio of the wheels. For example, Patent Document 1 discloses a driving torque distributed to each wheel based on the product of the slip ratio of each wheel and the driving stiffness of each corresponding wheel in order to improve the limit performance at the time of turning acceleration of the vehicle. A control device for determining a four-wheel drive vehicle has been proposed.

JP 2009-61888 A

  By the way, the relationship between the slip rate of the wheel and the driving force applied to the wheel is almost linear, and the region where the slip rate is very small (for example, the region where the slip rate is 8% or less. However, it is desirable to appropriately control the slip ratio of a wheel in a four-wheel drive vehicle in consideration of such a small slip region. In particular, in a four-wheel drive vehicle that changes the driving torque transmitted to the rear wheels by transmitting the driving torque to the rear wheels through the coupling and changing the coupling fastening torque, taking into account the minute slip region. It is preferable that the slip ratio of the wheel can be appropriately controlled by changing the coupling fastening torque.

  The present invention has been made to solve the above-described problems of the prior art, and appropriately controls the coupling torque of the coupling that transmits the driving torque to the rear wheels in consideration of the minute slip region. An object of the present invention is to provide a slip ratio control device for a four-wheel drive vehicle.

In order to achieve the above object, the present invention provides a slip ratio control device for a four-wheel drive vehicle that transmits a motor output torque output by a motor as a drive source of a vehicle to front wheels and rear wheels. The slip ratio control device for the driving vehicle transmits a part of the prime mover output torque to the rear wheel through the coupling, and transmits the coupling torque of the coupling to the rear wheel by changing the coupling torque of the coupling. Coupling slip ratio calculating means for determining a coupling slip ratio related to slip occurring in the coupling based on the front wheel speed and the rear wheel speed, and a driving torque transmitted to the rear wheel. Rear wheel slip ratio calculating means for calculating a rear wheel slip ratio related to slip occurring in the rear wheel based on the wheel driving torque and the driving stiffness. The front wheel slip ratio calculation for determining the front wheel slip ratio related to the slip occurring in the front wheel based on the coupling slip ratio determined by the coupling slip ratio calculation means and the rear wheel slip ratio calculated by the rear wheel slip ratio calculation means. And a fastening torque calculating means for obtaining a fastening torque to be applied to the coupling based on the front wheel slip ratio obtained by the front wheel slip ratio calculating means so that the front wheel slip ratio is maintained in a minute slip region. It possesses coupling control means for controlling the application of fastening torque the torque calculating means is determined the coupling, the micro slip region, the relationship between the driving force applied to the slip ratio and the wheel of the wheels substantially linear It is a region that can be regarded as a region .
In the present invention configured as described above, since a driving force is applied to the rear wheel, the rear wheel speed in the four-wheel drive vehicle in which the rear wheel speed cannot be referred to as the vehicle body speed is referred to. The coupling slip ratio is obtained from the front wheel speed, and the front wheel slip ratio is obtained based on the coupling slip ratio and the rear wheel slip ratio obtained from the rear wheel driving torque and the driving stiffness, and based on the front wheel slip ratio. Thus, since the fastening torque applied to the coupling is obtained, the front wheel slip ratio can be appropriately controlled. Specifically, by obtaining the fastening torque from the difference between the front wheel slip ratio and the target slip ratio and distributing the drive torque to the rear wheels, the slip ratio when the motor output torque is received only by the front wheels, The front wheel slip ratio can be arbitrarily controlled within the range up to the slip ratio when the motor output torque is received.

In the present invention, preferably, the fastening torque currently applied to the coupling, the gear ratio of the differential gear of the rear wheel, the gear ratio of the power take-off (PTO) that transmits the drive torque from the transmission to the propeller shaft, Rear wheel drive torque calculation means for obtaining rear wheel drive torque based on the motor output torque is further provided, and the rear wheel slip ratio calculation means is based on the rear wheel drive torque obtained by the rear wheel drive torque calculation means. Find the wheel slip rate.
According to the present invention configured as described above, the front wheel slip ratio generated in the front wheels can be obtained with high accuracy.

In the present invention, preferably, the fastening torque calculation means applies the prime mover output torque only to the front wheels when the prime mover output torque is applied to the front wheels and the front wheel slip ratio is within the minute slip region. Thus, when the front wheel slip ratio deviates from the minute slip area, the engagement torque is obtained so that the motor output torque is distributed to the rear wheels in order to return the front wheel slip ratio to the minute slip area. According to the present invention configured, the front wheel slip ratio can be more effectively maintained in the minute slip region.

In the present invention, it is preferable that the engagement torque calculation means obtains the engagement torque based on the accelerator opening change amount of the four-wheel drive vehicle in addition to the front wheel slip ratio obtained by the front wheel slip ratio calculation means.
According to the present invention configured as described above, it is possible to alleviate the delay in feedback control and improve the accelerator response.

  According to the slip ratio control device for a four-wheel drive vehicle of the present invention, the slip ratio of the front wheels is appropriately maintained within the minute slip region by controlling the coupling torque of the coupling that transmits the driving torque to the rear wheels. Can do.

1 is an overall configuration diagram schematically showing a vehicle to which a slip ratio control device for a four-wheel drive vehicle according to an embodiment of the present invention is applied. It is a functional block diagram of the controller by embodiment of this invention. It is explanatory drawing of a micro slip area | region. FIG. 3 is a block diagram of a model according to an embodiment of the present invention.

  Hereinafter, a slip ratio control device for a four-wheel drive vehicle according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[Device configuration]
First, an overall configuration of a vehicle to which a slip ratio control device for a four-wheel drive vehicle according to an embodiment of the present invention is applied will be described with reference to FIG. FIG. 1 is an overall configuration diagram schematically showing a vehicle to which a slip ratio control device for a four-wheel drive vehicle according to an embodiment of the present invention is applied.

  As shown in FIG. 1, the vehicle 1 mainly includes an engine 2, a transmission 3, a PTO (Power Take Off) 5, front drive shafts 7R and 7L, and a pair of left and right front wheels 9 (right A front wheel 9R and a left front wheel 9L), a pair of left and right rear wheels 10 (right rear wheel 10R and left rear wheel 10L), a propeller shaft 12, an electromagnetic coupling 13, a rear differential gear 15, a rear drive shaft 17R, 17L, controller 20, accelerator opening sensor 31, front wheel speed sensors 32R and 32L, and rear wheel speed sensors 33R and 33L.

  The vehicle 1 is a four-wheel drive vehicle based on a front engine / front drive system (FF system). Specifically, the vehicle 1 does not perform full-time four-wheel drive, but has a two-wheel drive state (a state in which only the front wheels 9 are driven) and a four-wheel drive state (both the front wheels 9 and the rear wheels 10). The state in which the motor is driven) can be switched as appropriate. The vehicle 1 is configured to steer the front wheels 9 in response to a steering operation (not shown).

The engine 2 burns a mixture of fuel and air to generate a driving torque (engine torque) as a driving force of the vehicle 1, and transmits this driving torque to the transmission 3. The transmission 3 is a transmission capable of changing a gear ratio in a plurality of stages, and transmits a driving torque from the engine 2 at a set gear ratio. In this case, the transmission 3 transmits the driving torque from the engine 2 to the front wheels 9 via the front drive shafts 7R and 7L and also to the PTO 5 corresponding to the transfer. The PTO 5 transmits drive torque from the transmission 3 to the propeller shaft 12, and the propeller shaft 12 transmits drive torque from the PTO 5 to the electromagnetic coupling 13. The electromagnetic coupling 13 transmits the driving torque from the propeller shaft 12 to the rear differential gear 15, and the rear differential gear 15 transmits the driving torque transmitted from the electromagnetic coupling 13 via the rear drive shafts 17R and 17L. To the right rear wheel 10R and the left rear wheel 10L.
Hereinafter, the driving torque output by the engine 2 is appropriately referred to as “PT (Power Train) output torque”. Strictly speaking, this PT output torque corresponds to the torque transmitted by the transmission 3 in the drive torque output by the engine 2. Further, the PT output torque corresponds to an example of “motor output torque” in the present invention.

Specifically, the electromagnetic coupling 13 is a coupling that connects the propeller shaft 12 and a shaft connected to the rear differential gear 15, and includes an electromagnetic coil, a cam mechanism, a clutch, and the like (not shown). The electromagnetic coupling 13 is configured to vary the fastening torque in the electromagnetic coupling 13 according to the current supplied to the internal electromagnetic coil under the control of the controller 20. By changing the fastening torque in this way, the electromagnetic coupling 13 is the maximum value of the driving torque transmitted from the propeller shaft 12 to the rear differential gear 15 (that is, the driving torque transmitted to the rear wheel 10). A certain maximum transmission torque can be changed. In this case, the electromagnetic coupling 13 functions to set a maximum transmission torque under the control of the controller 20 and to transmit a driving torque corresponding to the maximum transmission torque to the rear differential gear 15.
Specifically, the electromagnetic coupling 13 transmits the driving torque transmitted from the propeller shaft 12 to the rear differential gear 15 as it is, with respect to the driving torque equal to or less than the maximum transmission torque. On the other hand, the electromagnetic coupling 13 does not transmit all of the transmitted driving torque to the rear differential gear 15 for the driving torque that is transmitted from the propeller shaft 12 and exceeds the maximum transmitting torque, and corresponds to the maximum transmitting torque. Only the drive torque is transmitted to the rear differential gear 15.
In addition, the structure described in Unexamined-Japanese-Patent No. 2013-3260 can be applied to the electromagnetic coupling 13, for example.

  On the other hand, the accelerator opening sensor 31 detects an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) by the driver. The front wheel speed sensor 32R detects the wheel speed of the right front wheel 9R, and the front wheel speed sensor 32L detects the wheel speed of the left front wheel 9L. The rear wheel speed sensor 33R detects the wheel speed of the right rear wheel 10R, and the rear wheel speed sensor 33L detects the wheel speed of the left rear wheel 10L. The accelerator opening sensor 31, front wheel speed sensors 32R and 32L, and rear wheel speed sensors 33R and 33L respectively detect the detected accelerator opening, front wheel speed (the wheel speeds of the right front wheel 9R and the left front wheel 9L), and the rear wheel. Detection signals corresponding to the speeds (the wheel speeds of the right rear wheel 10R and the left rear wheel 10L) are output to the controller 20.

  Next, FIG. 2 shows a functional block diagram of the controller 20 according to the embodiment of the present invention. As shown in FIG. 2, the controller 20 functionally includes a coupling slip ratio calculator 21, a rear wheel drive torque calculator 22, a rear wheel slip ratio calculator 23, and a front wheel slip ratio calculator 24. The fastening torque calculation unit 25 and the coupling control unit 26 are included.

Here, the function of each component of the controller 20 will be briefly described (details will be described later).
The coupling slip ratio calculation unit 21 obtains a coupling slip ratio related to slip generated in the electromagnetic coupling 13 based on the front wheel speed and the rear wheel speed.
The rear wheel drive torque calculation unit 22 is a fastening torque currently applied to the electromagnetic coupling 13, a gear ratio of the rear differential gear 15 (hereinafter simply referred to as “rear differential gear ratio”), PT output torque, and PTO 5. The rear wheel drive torque which is the drive torque transmitted to the rear wheel 10 is obtained based on the gear ratio (hereinafter simply referred to as “PTO gear ratio”). In the case of a vehicle having the same rear differential gear ratio and PTO gear ratio, one value of the rear differential gear ratio and the PTO gear ratio may be used. In the case of a vehicle having a different rear differential gear ratio and PTO gear ratio, the rear differential gear ratio is used. Each value of the ratio and the PTO gear ratio may be used.
The rear wheel slip ratio calculating unit 23 applies the rear wheel driving stiffness to the rear wheel 10 based on the rear wheel driving stiffness defined in the minute slip region for the rear wheel 10 and the rear wheel driving torque obtained by the rear wheel driving torque calculating unit 22. The rear wheel slip ratio relating to the slip that has occurred is obtained.
The front wheel slip ratio calculation unit 24 generates a slip generated in the front wheel 9 based on the coupling slip ratio obtained by the coupling slip ratio calculation unit 21 and the rear wheel slip ratio obtained by the rear wheel slip ratio calculation unit 23. Obtain the front wheel slip ratio.
The fastening torque calculation unit 25 should be applied to the electromagnetic coupling 13 based on the front wheel slip rate obtained by the front wheel slip rate calculation unit 24 so that the front wheel slip rate is maintained in the minute slip region for the front wheel 9. Obtain the fastening torque.
The coupling control unit 26 performs control to apply the fastening torque obtained by the fastening torque calculation unit 25 to the electromagnetic coupling 13. Specifically, the coupling control unit 26 calculates the amount of current that flows through the electromagnetic coupling 13.

Thus, the controller 20 corresponds to the “slip rate control device for a four-wheel drive vehicle” according to the present invention.
Note that the controller 20 stores various programs (including basic control programs such as an OS and application programs that are activated on the OS to realize specific functions), programs, and various data that are interpreted and executed on the CPU. It is configured by a computer having an internal memory such as a ROM or RAM for storing. For example, the controller 20 is configured by an ECU (Electronic Control Unit).
Further, the controller 20 estimates the fastening torque currently applied to the electromagnetic coupling 13 based on the current value input to the electromagnetic coupling 13.

[Control method]
Next, the control method performed by the controller 20 in the present embodiment will be specifically described.

  Conventionally, traction control for suppressing idling of wheels has been performed. When performing traction control, a slip ratio defined by the wheel speed and the vehicle body speed is required, but it is difficult to measure the vehicle body speed. For example, there is a method of acquiring the vehicle body speed using the wheel speed of the non-driven wheel (rear wheel). However, this method cannot acquire the vehicle body speed for a four-wheel drive vehicle that originally has no non-driven wheel. . Therefore, in general, in a four-wheel drive vehicle, traction control is performed by acquiring a vehicle body speed using an acceleration sensor.

  As described above, when the slip ratio control is applied to the four-wheel drive vehicle, the rear wheel speed cannot be referred to as the vehicle body speed. By the way, in the vehicle 1 as a four-wheel drive vehicle, when the rear wheel speed is referred to, the relationship between the rear wheel speed and the front wheel speed corresponds to the coupling slip ratio of the electromagnetic coupling 13. . The coupling slip ratio of the electromagnetic coupling 13 indicates the degree of slip occurring between the two fastening members. The rotational speed of the propeller shaft 12 and the rotational speed of the rear differential gear 15 (for example, the rear differential gear 15) This corresponds to the ratio of the number of rotations of the connected shaft).

  The coupling slip ratio as described above is correlated with the slip ratio of the wheel. Therefore, the slip ratio of the wheel can be estimated from the coupling slip ratio. Therefore, in the present embodiment, the coupling slip ratio is obtained from the front wheel speed and the rear wheel speed, the front wheel slip ratio is obtained from the coupling slip ratio, and the front wheel slip ratio is within the minute slip region based on the front wheel slip ratio. Therefore, the fastening torque that should be applied to the electromagnetic coupling 13 is determined.

  Here, the minute slip region will be described in detail with reference to FIG. In FIG. 3, the horizontal axis indicates the slip ratio of the wheel, and the vertical axis indicates the driving force applied to the wheel. Graph G1 shows an example of the relationship between slip ratio and driving force on a road surface having a relatively high friction coefficient, and graph G2 shows the relationship between slip ratio and driving force on a road surface having a relatively low friction coefficient. An example is shown. As shown in the graphs G1 and G2, in the region R1 where the slip ratio is equal to or less than a predetermined value A1 (for example, 8%), the relationship between the slip ratio and the drive torque is substantially proportional, in other words, the slip ratio and the drive torque. It can be seen that the relationship is a linear function passing through the origin. In the present embodiment, such a region R1 is used as a minute slip region.

  The minute slip region can be defined for each of the front wheel 9 and the rear wheel 10, and the minute slip region for the front wheel 9 is appropriately referred to as a “front wheel minute slip region”, and the minute slip region for the rear wheel 10. Is appropriately referred to as a “rear wheel minute slip region”. The front wheel minute slip region and the rear wheel minute slip region substantially coincide with each other because the front and rear wheels are in the same road surface state in many traveling scenes, but are different in other cases. That is, the above-mentioned predetermined value A1 that defines the upper limit of the minute slip region is often the same value in the front wheel minute slip region and the rear wheel minute slip region, but assuming a traveling scene in which the road surface is different between the front and rear wheels. Will take different values.

Next, the control method according to the present embodiment will be described more specifically. First, symbols used in this specification are defined as follows.
V _v: vehicle speed V _f: front wheel speed V _r: rear wheel speed y _f: front wheel slip ratio y _r: rear wheel slip ratio y _c: coupling slip ratio T _c: engaging torque T _pt: PT output torque T _f: front wheel drive torque T _r: rear wheel drive torque k _f: front wheel driving stiffness k _r: rear wheel driving stiffness g _r: Riyadefugiya ratio g _f: PTO gear ratio I _f: front inertia r: tire size W _f: front wheel axle weight W _r : Rear wheel axle weight

The front wheel slip ratio y _f is expressed by equation (1) using the vehicle body speed V _v and the front wheel speed V _f . Originally, the slip ratio is divided by the wheel speed, but here, in order to simplify the calculation, a pseudo slip ratio divided by the vehicle body speed (hereinafter, this pseudo slip ratio is referred to as “slip ratio”) is used. . Further, the rear wheel slip ratio y _r is expressed by equation (2) using the vehicle body speed V _v and the rear wheel speed V _r . When the rear wheel speed V _r is solved in Expression (2), Expression (3) is obtained.
y _f = (V _f −V _v ) / V _v equation (1)
y _r = (V _r −V _v ) / V _v equation (2)
V _r = (1 + y _r ) V _v equation (3)

The relationship between the coupling slip ratio y _c of the electromagnetic coupling 13, a front wheel slip ratio y _f and the rear wheel slip ratio y _r is represented by the formula (4).
y _c = (V _f −V _r ) / V _r
= {1 / (1 + y _r )} {(V _f −V _v ) / V _v − (V _r −V _v ) / V _v }
= (Y _f −y _r ) / (1 + y _r ) Equation (4)
So
y _f = (1 + y _r ) y _c + y _r formula (5)
Thus, the front wheel slip ratio is calculated from the coupling slip ratio and the rear wheel slip ratio.

Engaging torque T _c that is currently applied to the electromagnetic coupling 13, it is possible to estimate the current value is inputted to the electromagnetic coupling 13, the rear wheel drive torque Tr is the fastening torque T _c and Riyadefugiya ratio g _r make use of,
T _r = g _r T _c (6)
It becomes. Further, the front wheel driving torque T _f at this time is obtained by using the PTO gear ratio g _f and the PT torque T _pt .
T _f = T _pt −g _f T _c (7)
It becomes.

Here, since the PTO gear ratio g _f and the rear differential gear ratio g _r are equal, assuming that the torque is evenly applied to the four wheels when the coupling slip ratio y _c is 0, the rear wheel drive torque T _r Is represented by equation (8) or equation (9), and the front wheel drive torque T _f is represented by equation (10).
T _r = T _pt / 2 (when g _r T _c ≧ T _pt / 2) Equation (8)
T _r = g _r T _c (when g _r T _c <T _pt / 2) Equation (9)
T _f = T _pt −T _r (10)

The relationship between the front wheel slip ratio y _f and front wheel drive torque T _f in a minute slip region, the ratio of the front wheel slip ratio y _f and front wheel drive torque T _f at the front wheel micro slip region (the inclination of the other words a linear function) The corresponding front wheel driving stiffness k _f is expressed by equation (11).
k _f ⁻¹ = T _f / ry _f formula (11)
Further, assuming that the rear wheels are in the same ground contact state, from the frictional expression “F = μN”, k _r = k _f W _r / W _f (12)
Deriving the rear wheel driving stiffness as
y _r = k _r ⁻¹ T _r formula (13)
The rear wheel slip ratio _yr is obtained as follows.

In this embodiment, the front wheel micro slip region where the relationship between the front wheel slip ratio y _f and front wheel drive torque T _f keeps a linear relationship is aimed to maintain the front wheel slip ratio y _f. Therefore, the rear wheel driving torque _Tr is changed in accordance with the deviation amount of the front wheel slip ratio y _f from the front wheel minute slip region. The amount of deviation of the front wheel slip ratio y _f when the vehicle 1 is not accelerating (that is, when the wheel slips and no propulsive force is generated) is calculated from the differential values of the equations (1) and (2) to the acceleration of the front wheels 9. equal. Therefore, the rear wheel driving torque change amount dT _r to change the rear wheel driving torque _Tr according to the deviation amount of the front wheel slip ratio y _f from the front wheel minute slip region is the inertia of the rotating system on the front side of the vehicle 1. This is expressed by equation (14) using the front inertia I _f shown.
dT _r = I _f (y _f −y _f ^* ) Equation (14)

In Expression (14), “y _f ^* ” is the target front wheel slip ratio. The target front wheel slip ratio y _f ^* corresponds to the front wheel slip ratio when the front wheel slip ratio is assumed to be in the front wheel minute slip region, and the front wheel driving stiffness k _f and the PT output torque T _pt are used to calculate “y _f ^* = K _f ⁻¹ T _pt ”. Substituting the equation for the target front wheel slip ratio y _f ^* and the above equation (4) into equation (14) yields equation (15). Then, a change amount (fastening torque change amount) dT _c of the fastening torque T _c corresponding to the rear wheel drive torque change amount dT _r of Equation (15) is expressed by Equation (16).
dT _r = I _f {(1 + y _r ) y _c + y _r −k _f ⁻¹ T _pt } Equation (15)
dT _c = (I _f / g _r ) {(1 + y _r ) y _c + y _r −k _f ⁻¹ T _pt } Equation (16)

Coupling slip ratio y _c and the rear wheel slip ratio y _r before and after each wheel speed V _f in the formula (16), so can be determined from V _r and a rear wheel drive torque T _r, the fastening torque of the formula (16) The change amount dT _c can be obtained. That is, it is possible to obtain the fastening torque change amount dT _c is an amount to be changed the current engaging torque T _c in order to maintain the front wheel slip ratio y _f on the front wheel micro slip region. The fastening torque T _c actually applied to the electromagnetic coupling 13 may be a torque obtained by adding a fastening torque change amount dT _c to the current fastening torque T _c .

[Control model]
Next, a specific example of a control model executed by the controller 20 in this embodiment will be described with reference to FIG. FIG. 4 shows a block diagram of a model according to an embodiment of the present invention.

First, the coupling slip ratio calculation unit 21 of the controller 20 acquires the wheel speed of the right front wheel 9R and the wheel speed of the left front wheel 9L detected by the front wheel speed sensors 32R and 32L, and the wheel speed of the right front wheel 9R and the left The average value of the wheel speed of the front wheel 9L is obtained as the front wheel speed _Vf , and the wheel speed of the right rear wheel 10R and the wheel speed of the left rear wheel 10L detected by each of the rear wheel speed sensors 33R and 33L are acquired. obtaining an average value of the wheel speed of the wheel speed and the left rear wheel 10L of the rear wheel 10R as the rear wheel speed V _r. And, the coupling slip ratio calculating unit 21, these front wheel speed V _f and the rear wheel speed V _r, using equation (4), determining the coupling slip ratio y _c.

Next, the rear wheel drive torque calculation unit 22 of the controller 20 calculates the fastening torque T _c currently applied to the electromagnetic coupling 13 and the PT output torque T _pt corresponding to the engine torque output by the engine 2. get. Then, the rear wheel drive torque calculation unit 22 multiplies the fastening torque T _c by the rear differential gear ratio g _r (= PTO gear ratio g _f ) and the PT output torque T _pt by 0.5 (T _pt / 2) and the smaller value is determined as the rear wheel drive torque _Tr . In other words, the rear wheel drive torque calculating section 22, in the case of _{"g r T c ≧ T pt /} 2 ", from equation (8), to determine the "T _pt / 2" as the rear wheel drive torque T _r, On the other hand, in the case of “g _r T _c <T _pt / 2”, “g _r T _c ” is determined as the rear wheel driving torque T _r from the equation (9).

Then, wheel slip rate calculating section 23 after the controller 20, the equation (13), the rear wheel reciprocal of the rear wheel driving stiffness k _r relative wheel drive torque T _r after the driving torque calculation unit 22 is calculated (k _The rear wheel slip ratio y _r is obtained by multiplying by _r ⁻¹ ).

Next, the front wheel slip rate calculation unit 24 of the controller 20 determines the coupling slip rate y _c obtained by the coupling slip rate calculation unit 21 and the rear wheel slip rate y _r obtained by the rear wheel slip rate calculation unit 23. based on, obtaining the front wheel slip ratio y _f. Specifically, the front wheel slip rate calculating section 24, based on the following equation obtained by transforming Equation (4) (17), obtains a front wheel slip ratio y _f.
y _f = (1 + y _r ) y _c + y _r (17)

On the other hand, the fastening torque calculation unit 25 of the controller 20 acquires the PT output torque T _pt corresponding to the engine torque output by the engine 2, and the reciprocal of the front wheel driving stiffness k _{f with} respect to the PT output torque T _pt . By multiplying (k _f ⁻¹ ), the target front wheel slip ratio y _f ^* is obtained. Then, the fastening torque calculator 25, this target front wheel slip ratio y _f ^*, based the front wheel slip ratio y _f of the front wheel slip ratio calculator 24 is determined, and Riyadefugiya ratio g _r, the front inertia I _f, Request fastening torque variation dT _c. Specifically, the fastening torque calculation unit 25 calculates “I _{f with} respect to a value obtained by subtracting the target front wheel slip rate y _f ^* from the front wheel slip rate y _f obtained by the front wheel slip rate calculation unit 24 from Expression (16). By multiplying by “g _r ⁻¹ ”, an engagement torque change amount dT _c is obtained.

Further, the fastening torque calculation unit 25 acquires the accelerator opening AP detected by the accelerator opening sensor 31 in parallel with the calculation processing of the engagement torque change amount dT _c as described above, and differentiates this accelerator opening AP. It was by multiplying a predetermined gain K with respect to the accelerator opening change amount dAP, obtaining the feedforward torque variation dT _FF for feedforward control of the tightening torque T _c. By using such a feedforward torque change amount dT _FF , it is possible to alleviate a delay in feedback control with respect to the engagement torque change amount dT _c and improve the accelerator response.

Then, the fastening torque calculation unit 25 adds the fastening torque change amount dT _c , the feedforward torque change amount dT _FF, and the current fastening torque T _{c according} to the following equation (18), so that the electromagnetic cup A fastening torque T _c to be applied to the ring 13 is obtained.
_{T c = dT c + dT FF} + T c formula (18)
Note that “T _c ” on the left side of Equation (18) is the fastening torque T _c to be applied to the electromagnetic coupling 13 (in other words, the fastening torque T _c obtained this time), and is included in the right side of Equation (18). “T _c ” is the current fastening torque T _c (in other words, the fastening torque T _c obtained last time).

Thereafter, the coupling control unit 26 of the controller 20 converts the fastening torque T _c obtained by the fastening torque calculation unit 25 into a current value, and supplies a current corresponding to the current value to the electromagnetic coupling 13. The fastening torque T _c is applied to the electromagnetic coupling 13.

[Function and effect]
According to the slip ratio control device for a four-wheel drive vehicle according to the embodiment of the present invention described above, the rear wheel speed V _f and the front wheel speed V _r are deliberately referred to by referring to the rear wheel speed V _f in the four-wheel drive vehicle. after asking coupling slip ratio y _c, based on the front wheel slip ratio y _f obtained from the coupling slip ratio y _c, so obtaining a fastening torque T _c to be applied to the electromagnetic coupling 13, the front wheel slip ratio y _f Can be controlled appropriately. Specifically, the front wheel slip ratio y _f can be appropriately maintained within the front wheel minute slip region. Thereby, it becomes possible to suppress the slip of a wheel appropriately.
Further, according to the present embodiment, the rear wheel drive torque is controlled only when the front wheel slip ratio deviates from the minute slip region, so that the transmission torque within the PTO 5 and the rear differential 15 and the fastening torque of the electromagnetic coupling 13 are generated. Current can be saved, and energy efficiency can be improved.

[Modification]
In the above-described embodiment, the present invention is applied to the vehicle 1 using the engine 2 as a drive source. However, the present invention is also applicable to a vehicle using a motor (electric motor) as a drive source, that is, an EV vehicle. .
In the above-described embodiment, the present invention is applied to the electromagnetically driven electromagnetic coupling 13. However, the present invention can be applied to various couplings such as a hydraulically driven coupling. It is.

1 Vehicle 2 Engine 3 Transmission 5 PTO
9 Front wheel 10 Rear wheel 12 Propeller shaft 13 Electromagnetic coupling 15 Rear differential gear 20 Controller 31 Accelerator opening sensor 32R, 32L Front wheel speed sensor 33R, 33L Rear wheel speed sensor

Claims (4)

A slip ratio control device for a four-wheel drive vehicle that transmits a prime mover output torque output by a prime mover as a vehicle drive source to front and rear wheels, the slip ratio control device for a four-wheel drive vehicle includes the prime mover output torque Is transmitted to the rear wheel through the coupling, and by changing the coupling torque of the coupling, the torque transmitted to the rear wheel among the motor output torque is variably configured.
A coupling slip ratio calculating means for determining a coupling slip ratio related to the slip occurring in the coupling based on the front wheel speed and the rear wheel speed;
Rear wheel slip ratio calculating means for calculating a rear wheel slip ratio related to slip occurring in the rear wheel based on a rear wheel driving torque that is a driving torque transmitted to the rear wheel and a driving stiffness;
Based on the coupling slip ratio obtained by the coupling slip ratio calculating means and the rear wheel slip ratio obtained by the rear wheel slip ratio calculating means, a front wheel slip ratio for obtaining a front wheel slip ratio relating to a slip occurring in the front wheel. A calculation means;
Fastening torque calculating means for obtaining a fastening torque to be applied to the coupling based on the front wheel slip ratio obtained by the front wheel slip ratio calculating means so that the front wheel slip ratio is maintained in the minute slip region;
Coupling control means for performing control to apply the fastening torque obtained by the fastening torque calculation means to the coupling;
I have a,
The slip ratio control device for a four-wheel drive vehicle, wherein the minute slip region is a region in which a relationship between a slip ratio of a wheel and a driving force applied to the wheel can be regarded as substantially linear . Based on the fastening torque currently applied to the coupling, the gear ratio of the differential gear of the rear wheel, the gear ratio of the power take-off that transmits the drive torque from the transmission to the propeller shaft, and the prime mover output torque, A rear wheel driving torque calculating means for obtaining the rear wheel driving torque;
The slip ratio control device for a four-wheel drive vehicle according to claim 1, wherein the rear wheel slip ratio calculating means obtains the rear wheel slip ratio based on the rear wheel drive torque obtained by the rear wheel drive torque calculating means. .   The fastening torque calculating means applies the prime mover output torque only to the front wheels when the prime mover output torque is applied to the front wheels and the front wheel slip ratio is within the minute slip region. When the front wheel slip rate departs from the minute slip region, the fastening torque is calculated so that the motor output torque is distributed to the rear wheels in order to return the front wheel slip rate to the minute slip region. The slip ratio control device for a four-wheel drive vehicle according to claim 1 or 2, wherein:   The fastening torque calculating means obtains the fastening torque based on an accelerator opening change amount of the four-wheel drive vehicle in addition to the front wheel slip ratio obtained by the front wheel slip ratio calculating means. The slip ratio control device for a four-wheel drive vehicle according to any one of the preceding claims.

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